Hermann Vogel studied astronomy at the Universities of Leipzig and Jena and then directed a private observatory for four years. He joined the staff of the Potsdam Astrophysical Observatory even before it opened in 1876, and served as its director from 1882 to 1907. Vogel made spectroscopic analyses of stars, planets, comets, and the sun. He was the first to demonstrate the sun’s rotation by measuring Doppler shifts of its receding and approaching limbs. He made detailed tables of the solar spectrum and attempted spectral classification of stars. Vogel’s most important work was photographic measurement of Doppler shifts to determine radial velocities of stars. He discovered one of the first spectroscopic binaries, and, with Julius Scheiner, made the first spectroscopic determination of stellar diameters and masses. He oversaw the design and construction of the Great Potsdam Refractor.